docs(forms): remove outdated ngForm selector deprecation notice (#35435)

In https://github.com/angular/angular/pull/33058, we removed support
for the `ngForm` selector in the NgForm directive. We deleted most
of the deprecation notices in that PR, but we missed a paragraph
of documentation in the API docs for NgForm.

This commit removes the outdated paragraph that makes it seem like
the selector is still around and deprecated (as opposed to removed),
as it might confuse users.

PR Close #35435

packages/forms/src/directives/ng_form.ts

@@ -55,24 +55,6 @@ const resolvedPromise = (() => Promise.resolve(null))();
  *
  * @usageNotes
  *
- * ### Migrating from deprecated ngForm selector
- *
- * Support for using `ngForm` element selector has been deprecated in Angular v6 and may be removed
- * in Angular v9 or later.
- *
- * This has been deprecated to keep selectors consistent with other core Angular selectors,
- * as element selectors are typically written in kebab-case.
- *
- * Now deprecated:
- * ```html
- * <ngForm #myForm="ngForm">
- * ```
- *
- * After:
- * ```html
- * <ng-form #myForm="ngForm">
- * ```
- *
  * ### Listening for form submission
  *
  * The following example shows how to capture the form values from the "ngSubmit" event.